1. Field of the Invention
This invention pertains to the in vitro radioimmunoassay of steroids present in serum.
2. Description of the Prior Art
Plasma steroid hormone clinical assay procedures often require time consuming, expensive, and precise laboratory manipulations. Plasma steroids have been measured by colorimetric (R. H. Silber and C. C. Porter, J. Biol. Chem., 210:923-932 (1954)), fluorimetric (D. J. Mattingly, J. Clin. Pathol., 15:374-378 (1962)), competitive protein binding (B. E. P. Murphy, J. Clin. Endocrinol. Metab., 28:343 et seq. (1968)), and radioimmunoassay (R. W. Farmer and C. E. Pierce, Clin. Chem., 20:411-414 (1974)) procedures, after organic solvent extraction. Any improvement of the assay procedure through the elimination of the preliminary extraction step is faced with the problem beset by the presence in the samples of carrier proteins competing with the antibodies. E. Rulleri, M. Zannino, S. Orlandini, and R. Malvano, Direct Radioimmunoassay of Plasma Cortisol, Clinica Chemica Acta, 66:319 to 330 (1976), point out "that direct assays in unextracted plasma have been reported, in which different techniques were adopted to circumvent protein effects, such as heat denaturation, incubation in an ethnolic medium, compensation for the protein content of samples, and protein inhibition by competition with massive amounts of steroids weakly cross-reacting with antibodies." However, these direct assay procedures still entail the use of a preliminary step prior to contacting the sample with the labeled steroid and antibody.